Tiling on a wooden sub floor

[barendjvrensburg]

I am about to tile my new bathroom with a wooden sub floor structure and want to make sure that my tiles or grout aren’t going to crack due to movement. Does the following sound like a good idea as a sub floor before I lay my tiles? On top of the wooden floor boards I’ll put a 12 mm backing board and on top of that I’ll put my tiles – would this be enough to prevent movement or should I put a layer of plywood first then backing board and then my tiles?

[thedoctor]

If the backing board is more flexible than the plywood then you need the plywood but 18mm would be better. Timber floors move a great deal and backing boards are there for greater adhesion rather than rigidity.